Pressurized fluid supply system



Dec. 20, 1966 HOFFMAN 3,292,415

PRESSURIZED FLUID SUPPLY SYSTEM Filed Jan. 27, 1964 2 Sheets-Sheet 1 OILQfiS OF 821 AIR/46c. BOTTOF CYL.

A INVENTOR. 559M190 A. /L/OFF/7/4/V ATTOP/VEXS 1956 B. L. HOFFMAN 3,292,415

PRESSURIZED FLUID SUPPLY SYSTEM Filed Jan. 27, 1964 2 Sheets-Sheet 2 I INVENTOR. 559M490 HOFFMAN United States Patent 3,292,415 PRESSURIZED FLUID SUPPLY SYSTEM Bernard L. Hoffman, Trenton, N.J., assignor to Frederick A. Krause Associates, Inc., Frenchtown, N.J., a corporation of New Jersey Filed Jan. 27, 1964, Ser. No. 340,439 13 Claims. (Cl. 72-453) This invention relates to hydraulic systems, and more particularly, to hydraulic pressure boosters of the type wherein air under pressure is utilized to pressurize hydraulic fluid for application in an operating unit.

Heretofore, systems of the class described have been devised wherein some external means have been required to effect transfer of hydraulic fluid or oil from an external reservoir to the oil pressure cylinder. Additionally, no means has been provided for sensing depletion of oil in the oil cylinder due to leakage, for example, so that loss of oil was only apparent upon failure of the booster to perform. Thus, where such conventional boosters were used to control the .action of dies and the like in punch presses, oil depletion was indicated by production of defective drawings which had to be scrapped.

Furthermore, once the oil is depleted the system must be recharged; and in conventional systems this was a manual operation that required as much as one half hour of down time for each recharging.

Such conventional systems made no provision for bleeding off excessive oil in the oil cylinder, thus contributing to severe damage to the hydraulic system in the event of development of a high back pressure capable of driving the air and oil pistons back to their extreme positions.

Accordingly, I have conceived by my invention a hydraulic system by which the foregoing difficulties and disadvantages are overcome, and in which I am able to sense oil depletion and to effect automatic or manual recharging of the system in about thirty seconds.

An important aspect of my invention resides in the combination of an air cylinder, a piston reciprocable in said cylinder, an oil cylinder, piston means in said oil cylinder movable with said piston, an oil reservoir, means supplying air under pressure to said air cylinder to move said piston means to protracted position relatively to said oil cylinder and to said oil reservoir, passageway means effecting fluid flow communication between said reservoir and oil cylinder upon such movement to charge said oil cylinder, means operable to vent the air under pressure in said air cylinder, means supplying air under pressure to said air cylinder on the other side of said piston to move same and said piston means in a direction to pressurize the oil in said oil cylinder, means bleeding off excessive oil from said oil cylinder, and high pressure outlet means in said oil cylinder to permit communication thereof with an external unit to be controlled.

More specifically, the oil piston means may be an extension of the air piston rod projecting through a cylinder head into the oil cylinder. As a feature of my invention, the aforesaid cylinder head may be suitably ported and formed to receive an annular retainer that is internally recessed and through which the piston rod passes, the rod being recessed as its free end to permit fluid flow therealong between the oil cylinder and an oil reservoir in fluid flow communication through the porting in the cylinder head to the recess in the retainer. This construction permits charging of the oil cylinder from the reservoir when the oil piston is protracted,, and also permits excess oil in the cylinder to bleed back to the reservoir when the oil is initially placed under pressure by retracting movement of the oil piston.

Another feature of my invention resides in the provision of sensing means which detects the depletion of "ice oil due to leakage, for example, prior to its complete exhaustion to a point at which damage can occur. In conjunction with this feature of the invention, I also provide a control system whereby the hydraulic boostercan be manually charged and operated; or which can respond to the aforesaid sensing means to shut off the external unit being operated by the'booster, recharge the booster, and reactivate the booster and external unit, all automatically.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, addition-a1 features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent construction as do not depart from the spirit and scope of the invention.

A specific embodiment of the invention has been chosen for purposes of illustraiton and description, and is shown in the accompanying drawings, forming a part of the specification, wherein:

FIG. 1 is a side elevation, partially in section of .a system incorporating the present invention;

FIG. 2 is a perspective view of a section of a hydraulic piston used in the system of FIG. 1;

FIGS. 3a and 3'1) are schematic representations of a control valve forming one unit the system of FIG. 1, said valve being shown in first and second operative position respectively;

FIG. 4 is an electrical schematic illustrating the wiring utilized in connection with the system of FIG. 1;

FIG. 5 is an enlarged view of a portion of the system of FIG. 1 during a particular interval in its operative sequence; and

FIG. 6 is an enlarged view of a portion of the system of FIG. 1 during a further interval in its operative sequence.

As shown in FIG. 1, a-system incorporating the present invention, includes upper and lower die holder members 12 and 14, mounted respectively, in upper and lower moveable elements of a press (shown in phantom outline). These upper and lower die holder members are each provided with a plurality of relatively moveable die elements 1624 which are shaped and positioned to interfit when the press is closed, thereby to produce a particular contour on a workpiece placed between the elements.

The various die elements are individually urged to extended positions by means of various pistons 26 and '28, operating under continuous hydraulic pressure. These pistons are of different diameters and therefore exert different forces when subjected to the same hydraulic pressure. Consequently, when the press is closed and the upper and lower die elements are forced against each other the pistons and the elements retract into their respective die holder members in a particular sequence, thus controlling the relative timing of formation of each .of the contours to be produced on the workpiece. This serves to minimize any stresses in the finished product and also improves the accuracy of the stamping or con-' tour forming operation.

The various pistons in the die holders are placed under continuous hydraulic pressure -by -fluid supplied through passageways 30 and 32 in the upper and lower die holder members 12 and 14. These passageways are connected to a fluid transmission line 34, which in turn is connected to a hydraulic multiplier unit 40 to be described below.

It will be appreciated that as the press closes to form a contoured stamping, the pistons 26 and 28 are forced to retracted position in the upper and llOWCI' die holder members 12 and 14 and thereby cause displacement of a certain amount of hydraulic fluid. In order to insure that the pistons will exert continuous force at all times during the stamping operation, it is necessary that the source of hydraulic supply be adequate to supply a constant pressure and at the same time to allow movement of hydraulic fluid out of the chambers occupied by the pistons as the pistons recede therein. Also, the inevitable loss of fluid which occurs due to Ileakage around the pistons, sink, etc. must not produce a loss of pressure.

The hydraulic multiplier unit 40, which operates to produce the desired flow of hydraulic fluid while maintaining constant pressure in the supply line, comprises essentially an upper air cylinder 42 and a lower hydraulic cylinder 44, the two cylinders being mounted in tandem on either side of a central housing 46. An air piston 48 is fitted to reciprocate under the influence of pneumatic pressure applied to the air cylinder 42. A connecting rod 50 extends down from the air piston, through the central housing 46 and forms a hydraulic piston 52 in the lower hydraulic cylinder 44. The air piston 48 is driven reciprocally within the air cylinder 42 by means of pneumatic pressure supplied from an external source (not shown). Such source may be for example, a conventional air pressure supply means of the type found in most industrial plants. This pressurized air is tapped off from an air supply line 54 and is passed through an air pressure limiter valve 56 to an accumulator 58 which acts as a constant pressure device, utilizing the elastic properties of air to permit a certain amount of displacement thereof, without producing appreciable change of pressure thereon. The pressurized accumulator air is supplied to the air cylinder 42 via a control valve 60 atmosphere and to the bottom of the air cylinder 42.. The inner rotor member 80 is provided with five equally which directs it so as to control the direction of movement of the air piston 48. The pneumatic forces thus produced on the air piston are transferred through the connecting rod 50 to the hydraulic piston 52 so as to maintain pressure control in the hydraulic portion of the system. The air piston 48, as shown is of larger diameter than the hydraulic piston. Thus there is provided a multiplying effect whereby the resulting pressure in the hydraulic cylinder 44 exceeds the pneumatic pressure in the air cylinder 42 by a number of times equal to the ratio of the respective areas of the air piston 48 and the hydraulic piston 52. A1180, this induced hydraulic pressure is maintained even during the displacement of hydraulic fluid which takes place during the retraction of the pistons '26 and 28 in the die holder members 12 and 14. This is because such fluid displacement merely causes movement of the hydraulic piston 52 and the air piston 48 against the relatively elastic pressurized air in the accumulator 58.

An important feature of the present invention resides in the manner in which the hydraulic fluid, which inevitably [leaks out between the various moving parts in any hydraulic system, is prior to the onset of dangerous operating conditions, automatically yet accurately, replenished without excessive delay. In accordance with this feature of the invention there is provided a hydraulic fluid supply reservoir 62 attached to one side of the air cylinder 42. The outlet of this reservoir communicates with the interior of the central housing 46 through a fluid passage 64 formed therein. The central housing in turn is provided with an insert member 66 shaped to form an annular cavity 68 surrounding the connecting rod 50. The cavity 68 communicates with the fluid passage 64 to the fluid supply reservoir and is pressure isolated from both the pneumatic and hydraulic cylinders 36 and 44 by means of upper and lower annular seals 70 and 72 which per- 4 mit slida-ble but sealing tight longitudinal movement of the connecting rod 50.

Referring now to FIG. 2, it will be seen that the hydraulic piston is provided with a bore 74 extending longitudinally upward from its lower end. A plurality of circunieferentially displaced slots 76 connect the longitudinal bore with the lateral surface of the piston at a small distance from its lower end. In all but the uppermost position of the piston, the hydraulic cylinder is sealed off from the annular cavity 68 and the supply reservoir by means of the hydraulic piston 52 and/or its connecting rod 50. However, when the piston reaches,

pressure air from the accumulator 58 to the top and bottom of the air cylinder 42 and to the hydraulic fluid supply reservoir 62. The valve may take any of several structural forms well known to those skilled in the art. FIGS. 3a and 3b show, in schematic arrangement,

one possible form of the control valve arranged to provide the necessary valving action. As shown, there is provided an outer stationary housing 78, of annular configuration, and within which rotates an inner rotor member 80. The outer stationary housing 78 is provided with five passageways 82-90 extending therethroughl at points equally displaced about the housing. These pas,-

sageways are connected respectively as indicated to the top of the hydraulic supply reservoir 62, to the air accumulator 58, to the top of the air cylinder 42, to the displaced openings 92-100 about its circumference, the first three of which 92, 94 and 96 are mutually interconnected within the inner rotor member, and the last two of which 98 and 100 are mutually interconnected in similar fashion. The inner rotor member 80 is displaceable between a first position as shown in FIG. 3a and a second position rotated 72 degrees in a counter clockwise direction as shown in FIG. 3b. In the first position, the accumulator 58 is connected directly to the draulic reservoir 62 and the bottom of the air cylinder 42 are placed into communication with the atmosphere.

A solenoid 102 is provided at the top of the hydraulic multiplier unit 40 and is connected to the inner rotor member of the control valve 60 in such a manner that the solenoid, when energized, moves the inner rotor member 80 to its second position (FIG. 3b), and when deenergized, causes the inner rotor member to its first position (FIG. 3a).

There is also provided within the central housing 46,

a micro-switch 104 having normally opened contacts arranged to be closed by movement of the air piston 48 to its lowermost position. This is accomplished by means of a buttom element 106 which-extends into the lower portion of the air cylinder so as to be contacted 104 are connected in series with first and second contacts 108 and 110 of a manual-automatic switch 111, a relay 112, and a pair of normally closed thermal delay relay contacts 114, across a pair of electrical supply lines 116. The relay 112 when energized, closes first and second pairs of normally opened contacts 118 and 120 and opens a third set of normally closed contacts 122. The first pair of relay contacts 118 are connected in series with the control valve solenoid 102 also across the electrical supply lines 116. A start switch 124 and a fuse 126 are located along the supply lines in series circuit relation with all of the other electrical elements. The second pair of relay contacts 120 are connected to bridge the contacts of the micro-switch 104 when the relay 112 is energized, while the third pair of contacts 122 are arranged to interrupt press operation during this time. A thermal delay relay 130 is connected to bridge both the first mentioned relay 112 and the thermal delay relay contacts 114 and operates to open these contacts after given time (approximately 30 seconds) following energization of the relay. The first contact 108 of the manval-automatic switch 111 is manually moveable between its said second contact 120 and a third contact 132 connected to a point between the solenoid 102 and the first pair of relay contacts 118.

During operation of the system, the hydraulic fluid reservoir 62 is partially filled with oil or other hydraulic fiuid, the level of which may be visibly indicated by means of a glass 134 on the side thereof. Air from the supply line 54 is applied to the accumulator 58, and with the control valve 60 in its normal or first position as shown in FIG. 3a, this air pressure is directed to the top of the air piston 48 forcing it and the connecting rod 50 downwardly to cause protract-ion of the hydraulic piston 52. This maintains hydraulic pressure in the passageways 30 and 32 of the upper and lower dieholder members 12 and 14, and the press is closed in the usual manner. As indicated previously, the closing force of the press causes the die members and their associated pistons to retract in any order of sequence determined by the relative diameters of the various pistons. Thus, as indicated in FIGS. 1 and 5, which show the pistons and die elements for the opened and closed positions of the press, respectively, it will be noted that in closing the larger upper piston 26 causes its upper die element 16 to force down against a lower die element 22 so that its smaller diameter piston 28 becomes retracted. When this piston reaches its lowermost positions in the lower die member 14 it then transmits full press force rather than hydraulic force and thus acts to produce retraction of the upperdie member 12 and its piston 26. This movement is upward relative to the outermost upper die element 18 which continues to descend thus producing firstly an initial bend 136 in a workpiece 138, and secondly, a subsequent bend 190. The outermost lower die element 24 is urged upwardly by further pistons (not shown) also exposed to the hydraulic pressure. As the upper and lower die holder members 12 and and 14 separate during opening of the press the outermost lower die element 24 rises while the innermost upper die element 16 descends. The lower element is provided with a concave rimming groove 142 which catches on the edge of the workpiece 138 during this relative movementand causes it to curl in the manner illustrated in FIG. 6. Further opening of the press allows the lower pistons 28 to extend and their die elements 22 to lift the now contoured workpiece out from the other died elements.

During the entire pressing and releasing sequence the hydraulic pressure on the various pistons is maintained by the multiplier unit 40, while the retraction and extension of the pistons causes the hydraulic piston 52 and the air piston 48 of the hydraulic unit to move up and down against the air pressure supplied from the accumulator 58.

As small amounts of oil or hydraulic fluid are lost the air piston 48 and hydraulic piston 52 becomes lower until a point is reached where the air piston 48 touches and closes the contact of the micro-switch 104. This connects the relay 112 across the electrical supply lines 116 causing -it to be energized so as to close its normally opened first and second pairs of contacts 118 and 120 and to open its normally closed third pair of contacts 122. As a result, operation of the press ceases and the control valve solenoid 10-2 becomes energized to switch the control valve 60 to its second position, as shown in FIG. 3b.

In this position of the control valve, the high air pressure output of the accumulator 58 is directed to the bottom of the air cylinder while the top of the cylinder is opened to the atmosphere so that the pistons 26 and 28 are urged in an upward direction. At .the same time, the high .air pressure output of the accumulator is also applied to the hydraulic fluid reservoir 62, placing the fluid therein under positive pressure.

Although the air piston 48 is thus moved off the microswitch 104 neither the relay 91 nor the solenoid 102 become de-energized, for the second pair of relay contacts 120 serve to electrically lock the relay 112 in its energized condition.

When the air piston 48 approaches the top of the air cylinder 42, the circu-m-ferentially displaced slots 76 in the hydraulic piston 52 come into alignment with the annular cavity 68 and the fluid passage 64. This places the now pressurized hydraulic fluid supply reservoir into communication with the interior of the hydraulic cylinder. Hydraulic fluid under pressure is then forced -firom the supply reservoir into the hydraulic cylinder. It may be noted that while more hydraulic fluid will be admitted if at the time this action takes place the press is opened and the various pistons 26 and 28 in the die holder members are extended, the refilling operation can still quite successfully be undertaken where the press is closed and the pistons are retracted.

The thermal delay relay permits the pistons 48 and 52 in the hydraulic unit 40 to remain in their upper or fluid replenishing positions for a given delay period sufficient to refill the hydraulic system, which as stated, is approximately thirty seconds. At the end of this time, the thermal relay contacts 114 are opened, thus de-energizing the relay 112. This opens the first and second pairs of relay contacts 118 and 120, de-energizing the control valve solenoid 102 and removing the electrical interlock from the relay 112. The third pair of relay contacts 122 during operation of the press the average positions of is closed and the press returns to normal operation. With the de-energization of the control valve solenoid 102, the control valve 60 returns to its first position, removing pressure from the hydraulic fluid reservoir 62 and reversing the application of pressure to the top of the air cylinder 42, so that the air and hydraulic pistons 48 and 52 are forced downwardly.

It is important to note that hydraulic pressure is vnot immediately built up; but rather, as the pistons descend, any excess hydraulic fluid in the system passes back through the bore and slots 74 and 76 in the hydraulic piston 52, the annular opening 68 in the insert 66, and the passage 64 in the central housing 46 to the now nonpressurized hydraulic fluid reservoir 62. Only after the slots 76 pass below the lower seal 72 does the unit begin to develop positive hydraulic pressure in the system. Thus, it will be appreciated that there is provided an automatic limiting action whereby the hydraulic system is refilled easily yet precisely to a proper level before full pressure is restored to the system by the multiplier unit. This automatic limiting action moreover, continues even during operation of the hydraulic press itself. For example, when the system is replenished With hydraulic fluid, the die holder members are normally opened and their pistons 26 and 28 are extended, thus creating additional space for injection of an excess of hydraulic fluid. Upon completion of the filling operation the hydraulic press, with this excess fluid is immediately put into regular operation. When the die holder members close and their pistons 26 and 28 are initially retracted, the excess fluid is forced back into the hydraulic cylinder 44, raising its piston 52. If the fluid quantity should happen to be too great the hydraulic piston will rise to a point Where the slots 76 into alignment with the opening 68 in the insert 66 and the excess fluid flows back into the reservoir. 62, thus precisely and automatically apportioning a proper amount of oil to the system. Also, during the time that the piston slots 76 are in alignment with the cavity 68, the hydraulic pressure immediately drops to that within the fluid reservoir 62 without dangerof aspiration of air into the system. The significance of this effect lies in the fact that the possibility of forcibly ramming the pneumatic piston 48 against the top of its cylinder by sudden back pressure is thereby eliminated.

The system may be replenished with hydraulic fluid at any time prior to complete downward movement of the pistons simply by throwing the manual-automatic switch 111 so that its first contact 108 touches its third contact 132. This acts to complete a circuit bypassing the normally opened relay contacts 118 and thereby energizes the solenoid 102. The solenoid then immediately switches the control valve 60 so that pressurized air is directed in the manner explained to move the pistons up to a hydraulic cylinder filling position. Pressurized air applied to the reservoir 62 then forces fluid from the reservoir into the hydraulic cylinder in a continuous manner until the first and third mode switch contacts 108 and 132 are parted.

It will be appreciated that the arrangement embodying the present invention issimple in structure requiring few moving parts and yet providing maximum pressure at the proper times. Because of the partciular construction involved, a valving action takes place between the hydraulic piston 52 and the insert element 66 without requiring the passage of the end of the piston across the lower oil seal 72. This reduces strain and wear on such seal and greatly increases the dependable life of the device.

Having thus described my invention with particular reference to the preferred form thereof, it will be obvious to those skilled in the art to which the invention pertains, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit and scope of my inventioin, as defined by the claims appended thereto.

What is claimed as new and desired to be secured by Letters Patent is:

1. An automatically self replenishing system for maintaining a supply of fluid at a given pressure, said system comprising a hydraulic cylinder, piston means movable into said cylinder for developing fluid pressure therein, an hydraulic fluid reservoir, valve means between said reservoir and said hydraulic cylinder, said valve means being openable responsive to said piston attaining a given retracted position relative to said cylinder, reversible driving means arranged to drive steadily against said piston for urging same into said cylinder, means for controlling said driving means, said controlling means including means for sensing the attainment by said piston of a given protracted position relative to said cylinder, and means responsive to said sensing means for reversing the direction of said driving means to move said piston to said given retracted position.

2. A self replenishing system as in claim 1 wherein there is provided a circumferential fluid seal positioned at a given point within said hydraulic cylinder in slidable sealing tight relation to said piston means, and wherein said piston is provided with an internal passage which opens on opposite sides of said seal When said piston is in its retracted position. v

3. A self replenishing system as in claim 1 wherein said valve means comprises means for bleeding olf excess oil from said hydraulic cylinder. I

4. A self replenishing system as in claim 1 wherein said valve means includes meansforming a passageway inside said piston and opening to the surface thereof at displaced locations therealong, a circumferential fluid seal fitting closely about said piston where it enters said cylinder and conduit means extending from said reservoir to an outlet located outside said seal at a position whereby it comes into alignment with one, of said passageway openings when said piston is in a retracted position, the other opening remaining inside said circumferential seal in said retracted position.

it 5. A self replenishing system as in claim 1 wherein said reversible drive means comprises a double acting air cylinder having an air piston therein connected to move said piston means, and wherein said means responsive to said. sensing means comprises a switchable air control means.

arranged to control the application of pressurized air to different sides of said air piston.

6. A self replenishing system as in claim 5 wherein said switchable air control means includes conduit means arranged in one switched condition to supply pressurized.

air against one side of the piston in said air cylinder to urge said piston means into said hydraulic cylinder while exposing the other end of said air cylinder to lower pressures, and in the other position to reverse the application of pressure to the piston in said air cylinder and to supply pressurized air to said reservoir.

7. In a system of the class described including a double acting air piston and cylinder assembly, an oil piston.

and cylinder assembly in tandem therewith, means admitting air under pressure to said air cylinder to shift said oil piston to a retracted position, an oil reservoir, -passageway means between said reservoir and oil cylinder, means applying air under pressure to oil in said reservoir when said oil piston is retracted to cause oil to flow through said passageway to said oil cylinder to charge same solenoid arranged to be energized by the closing of said circuit to control an air valve which thereby directs pressurized air to said air cylinder to shift said hydraulic piston to its said retracted position.

8. The system defined in claim 7 further including time delay means arranged to be energized with energization of said solenoid and operative to effect de-energization of said solenoid at a given time thereafter.

9. An automatically self replenishing system for main taining a supply of fluid at a given pressure, said system comprising a double acting air cylinder having an air piston fitted therein for movement under applied pressure, a hydraulic cylinder having a hydraulic piston enter: able therein, means interconnecting said pistons for move-:

ment in unison whereby said hydraulic piston is moved to a retracted position in its cylinder when said air piston is l at one end of its cylinder and is moved to a protracted position in its cylinder when said air piston is at the other end of its cylinder, air control means associated with said air cylinder and operative in first and second positions. to urge said airpiston under pressure toward said one end and said other end of its cylinder respectively, a hy-' draulic fluid reservoir, fluid passage means including hy draulic valve means between said fluid reservoir and said hydraulic cylinder, said valve means being arranged to be opened by said hydraulic piston in its retracted position, and time delay switch means arranged to be actuated when there has occurred a given amount of movement of said hydraulic piston toward its said protracted position to switch said air control means to its first position for a given length of time and subsequently to switch said air control means to its second position. i

10. An automatically self replenishing system for maintaining a supply of fluid at a given pressure, said system comprising a double acting air cylinder having an air piston fitted therein for movement under applied pressure, a hydraulic cylinder having a hydraulic piston enterable therein, means interconnecting said pistons for movement in unison whereby said hydraulic piston is moved to a retracted position in its cylinder when said pneumatic piston is near one end of its cylinder and is moved to a protracted position in its cylinder when said pneumatic piston is at the other end of its cylinder, air control means associated with said air cylinder and operative in first and second position to urge said air piston under pressure toward said one end and toward said other end of its cylinder respectively, a hydraulic fluid reservoir, hydraulic valve means between said reservoir and said hydraulic cylinder, said valve means arranged to be opened by said hydraulic piston in its retracted position, and switch means arranged to be actuated when there has occurred a given amount of movement of said hydraulic piston toward its said protracted position to switch said pneumatic control means to its said first position.

11. An automatically self replenishing system for main taining a supply of fluid at a given pressure, said system comprising a double acting air cylinder having an air piston fitted therein for movement under applied pressure, a hydraulic cylinder having a hydraulic piston enterable therein, an oil seal located within said hydraulic cylinder at a given distance from the end thereof into which said hydraulic piston enters, said oil seal surrounding said hydraulic piston to permit longitudinal and sealing tight movement of said hydraulic piston, means interconnecting said pistons for movement in unison whereby said by draulic piston is moved to a retracted position in its cylinder when said pneumatic piston is near one end of its cylinder and is moved to a protracted position in its cylinder when said pneumatic piston is at the other end of its cylinder, said hydraulic piston being provided with an internal passage which opens on each side of said seal when said hydraulic piston is in its said retracted position, air control means associated with said air cylinder and operative in first and second positions to urge said air piston under pressure toward said one end and toward said other end of its cylinder respectively, a hydraulic fluid reservoir, fluid passage means extending from said fluid reservoir to a point in said hydraulic cylinder in communication with said hydraulic piston on the air cylinder side of said oil seal whereby said fluid reservoir is placed into communication with said hydraulic cylinder via said internal passage when the hydraulic piston is in its said retracted position, and switch means arranged to be actuated when there has occurred a given amount of movement of said hydraulic piston toward its said protracted position to switch said pneumatic control means to its said first position.

12. An automatically self replenishing system for maintaining a supply of fluid at a given pressure, said system comprising, an air cylinder, a hydraulic cylinder, first and second piston means interfitted respectively into each of said cylinders and mutually interconnected to move in unison within said cylinders, first and second fluid passage means communicating with each end respectively of said air cylinder, air control valve means operative in a first position to direct a compressible fluid media under pressure into said air cylinder via said first passage means while venting said air cylinder via said second passage means to drive said first and second piston means in one direction, and operative in a second position to reverse the direction of compressible fluid media flow to drive said piston means in the opposite direction, inlet and outlet fluid passage means constructed to direct an incompressible fluid into and out of said hydraulic cylinder, said inlet fluid passage means being located to be sealed from said hydraulic cylinder by said second piston means when said second piston means moves in said one direction beyond a first given point, and switch means arranged to be actuated when there has occurred movement of said piston means in said one direction beyond a second given point to switch said pneumatic valve means to its said second position.

13. In a punch press provided with a die engageable with a workpiece upon operation of the press, a piston and cylinder assembly arranged to cooperate with said die to maintain same in selected positions during operation of the press, a hydraulic system including an air cylinder, a piston reciprocally movable in said air cylinder, an oil cylinder, oil piston means in said oil cylinder and movable by movement of said air piston, an oil reservoir, conduit means including valve means for effecting fluid flow communication between said reservoir and said oil cylinder upon movement of said oil piston to a given retracted position, switchable air control means connected to said air cylinder for directing the application of air pressure to difierent sides of said air piston and switch means arranged to respond to movement of said air piston to a position commensurate with a given protracted position of said oil piston to eifect switching of said air control means.

References Cited by the Examiner UNITED STATES PATENTS 825,301 7/1906 Coddington 54.5 2,075,235 3/ 1937 Sciaky 6054.5 2,324,149 7/1943 Gray 6054.5 2,740,258 4/ 1956 Weber 6054.5 3,085,530 4/ 1963 Williamson 6054.5 3,147,722 9/ 1964 Williamson 72-35 1 3,170,229 2/ 1965 Wenger.

CHARLES W. LANHAM, Primary Examiner.

RICHARD J. HERBST, Examiner. 

1. AN AUTOMATICALLY SELF REPLENSHING SYSTEM FOR MAINTAINING A SUPPLY OF FLUID AT A GIVEN PRESSURE, SAID SYSTEM COMPRISING A HYDRAULIC CYLINDER, PISTON MEANS MOVABLE INTO SAID CYLINDER FOR DEVELOPING FLUID PRESSURE THEREIN, AN HYDRAULIC FLUID RESERVOIR, VALVE MEANS BETWEEN SAID RESERVOIR AND SAID HYDRAULIC CYLINDER, SAID VALVE MEANS BEING OPENABLE RESPONSIVE TO SAID PISTON ATTAINING A GIVEN RETRACTED POSITION RELATIVE TO SAID CYLINDER, REVERSIBLE DRIVING MEANS ARRANGED TO DRIVE STEADILY AGAINST SAID PISTON FOR URGING SAME INTO SAID CYLINDER, MEANS FOR CONTROLLING SAID DRIVING MEANS, SAID CONTROLLING MEANS INCLUDING MEANS FOR SENSING THE ATTAINMENT BY SAID PISTON OF A GIVEN PROTRACTED POSITION RELATIVE TO SAID CYLINDER, AND MEANS RESPONSIVE TO SAID SENSING MEANS FOR REVERSING THE DIRECTION OF SAID DRIVING MEANS TO MOVE SAID PISTON TO SAID GIVEN RETRACTED POSITION. 